Androgen Receptor Roles in Spermatogenesis and Fertility: Lessons from Testicular Cell-Specific Androgen Receptor Knockout Mice Ruey-Sheng Wang, Shuyuan Yeh, Chii-Ruey Tzeng, and Chawnshang Chang George Whipple Laboratory for Cancer Research (R.-S.W., S.Y., C.C.), Departments of Urology and Pathology, University of Rochester Medical Center, Rochester, New York 14642; and Graduate Institute of Clinical Medicine (R.-S.W., C.-R.T.), College of Medicine, Department of Gynecology and Obstetrics, Taipei Medical University, Taipei 110, Taiwan Androgens are critical steroid hormones that determine the expression of the male phenotype, including the outward de- velopment of secondary sex characteristics as well as the ini- tiation and maintenance of spermatogenesis. Their actions are mediated by the androgen receptor (AR), a member of the nuclear receptor superfamily. AR functions as a ligand-de- pendent transcription factor, regulating expression of an ar- ray of androgen-responsive genes. Androgen and the AR play important roles in male spermatogenesis and fertility. The recent generation and characterization of male total and con- ditional AR knockout mice from different laboratories dem- onstrated the necessity of AR signaling for both external and internal male phenotype development. As expected, the male total AR knockout mice exhibited female-typical external ap- pearance (including a vagina with a blind end and a clitoris- like phallus), the testis was located abdominally, and germ cell development was severely disrupted, which was similar to a human complete androgen insensitivity syndrome or testic- ular feminization mouse. However, the process of spermato- genesis is highly dependent on autocrine and paracrine com- munication among testicular cell types, and the disruption of AR throughout an experimental animal cannot answer the question about how AR in each type of testicular cell can play roles in the process of spermatogenesis. In this review, we provide new insights by comparing the results of cell-specific AR knockout in germ cells, peritubular myoid cells, Leydig cells, and Sertoli cells mouse models that were generated by different laboratories to see the consequent defects in sper- matogenesis due to AR loss in different testicular cell types in spermatogenesis. Briefly, this review summarizes these re- sults as follows: 1) the impact of lacking AR in Sertoli cells mainly affects Sertoli cell functions to support and nurture germ cells, leading to spermatogenesis arrest at the diplotene primary spermatocyte stage prior to the accomplishment of first meiotic division; 2) the impact of lacking AR in Leydig cells mainly affects steroidogenic functions leading to arrest of spermatogenesis at the round spermatid stage; 3) the im- pact of lacking AR in the smooth muscle cells and peritubular myoid cells in mice results in similar fertility despite de- creased sperm output as compared to wild-type controls; and 4) the deletion of AR gene in mouse germ cells does not affect spermatogenesis and male fertility. This review tries to clarify the useful information regarding how androgen/AR functions in individual cells of the testis. The future studies of detailed molecular mechanisms in these in vivo animals with cell-spe- cific AR knockout could possibly lead to useful insights for improvements in the treatment of male infertility, hypogo- nadism, and testicular dysgenesis syndrome, and in attempts to create safe as well as effective male contraceptive methods. (Endocrine Reviews 30: 119 –132, 2009) I. Introduction II. Generation of Various Testicular Cell-Specific Androgen Receptor (AR) Knockout Mice III. Serum Testosterone Levels in Various Testicular Cell-Spe- cific AR Knockout Mice A. Testosterone biosynthesis in the Leydig cells B. Leydig cell development and maturation C. Tfm mice and humans with AIS D. T-AR -/y mice E. S-AR -/y mice F. L-AR -/y mice G. PM-AR -/y mice and G-AR -/y mice IV. Phenotypes of External Genitalia and Internal Male Ac- cessory Genital Organ Size in Various Testicular Cell- Specific AR Knockout Mice V. Testis Position in Various Testicular Cell-Specific AR Knockout Mice VI. Testis Size in Various Testicular Cell-Specific AR Knock- out Mice A. S-AR -/y mice B. Tfm mice and T-AR -/y mice C. L-AR -/y mice, PM-AR -/y mice, and G-AR -/y mice VII. Testis Morphology, Epididymal Sperm Count, and Fer- tility Test in Various Testicular Cell-Specific AR Knockout Mice A. Humans with AIS, Tfm mice, and T-AR -/y mice B. S-AR -/y mice C. L-AR -/y mice First Published Online January 27, 2009 Abbreviations: ACTB, -Actin; AIS, androgen insensitivity syn- drome; AMH, anti-Mu ¨ llerian hormone; AR, androgen receptor; AR -/y , AR knockout male; AR +/y , wild-type AR male; AR +/+ , wild-type AR female; CAIS, complete androgen insensitivity syndrome; Cre, cre re- combinase; DHT, 5-dihydroxytestosterone; floxed, flanked by lox site; G-AR -/y , germ cell-specific AR knockout; 3-HSD, 3-hydroxysteroid dehydrogenase; 17-HSD, 17-hydroxysteroid dehydrogenase; L-AR -/y , Leydig cell-specific AR knockout; LHR, LH receptor; PM, peritubular myoid; PM-AR -/y , PM cell-specific AR knockout; P450c17, 17-hydrox- ylase or 17,20 lyase; P450scc, P450 side-chain cleavage; RLF, relaxin-like factor; S-AR -/y , Sertoli cell-specific AR knockout; StAR, steroidogenic acute regulatory protein; T-AR -/y , total AR knockout; Tfm, testicular feminization; TSP-2, thrombospondin type 2. Endocrine Reviews is published by The Endocrine Society (http:// www.endo-society.org), the foremost professional society serving the endocrine community. 0163-769X/09/$20.00/0 Endocrine Reviews 30(2):119 –132 Printed in U.S.A. Copyright © 2009 by The Endocrine Society doi: 10.1210/er.2008-0025 119